To the Editor: Peste des petits ruminants (PPR) is a highly
infectious disease of small ruminants, characterized by high rates of
illness and death and caused by a single-stranded RNA virus (peste des
petits ruminants virus [PPRV]). PPRV can be divided into 4 genetically
distinct lineages based on the nucleocapsid (N) gene (1). The lineages
correlate well with geographic distribution of the virus, with lineages
I and II mainly restricted to western and central Africa, lineage III to
eastern Africa and the Arabian peninsula, and lineage IV to Southeast
Asia, the Middle East, and more recently northern Africa (2).

PPRV is endemic to most of western Africa, and considered a major
constraint on the livestock industry. In Sierra Leone, a country
bordered by Guinea, Liberia, and the Atlantic Ocean, and having high
goat and sheep populations, PPRV is believed to be the cause of
outbreaks of respiratory disease with high death rates. Inadequate
veterinary infrastructure and diagnostic capacity, exacerbated by the
civil war in 1991-2002, however, has prevented confirmation. In this
study, we confirmed presence of PPRV in Sierra Leone, which led to the
official report of PPR to the World Organisation for Animal Health
(Paris, France).

The study was conducted in April 2009 as part of a training mission
organized at Teko Central Veterinary Laboratory, Makeni, Sierra Leone,
by the World Organisation for Animal Health Collaborating Centre for
Biotechnology-based Diagnosis of Infectious Diseases in Veterinary
Medicine (www.sva.se/oie-cc) in collaboration with the Food and
Agriculture Organization-Emergency Center for Transboundary Animal
Diseases, Bamako, Mali. During the training, blood and serum samples
were collected from goats (n = 9) and sheep (n = 1) from 2 smallholders
with suspected outbreaks of PPR in the area around Makeni in central
Sierra Leone. In addition, serum from 5 goats with respiratory disease
was sampled at a livestock market in Kabala 100 km north of Makeni.

Serologic testing was performed at Teko. All serum samples (n = 15)
were tested for PPRV antibodies by using a commercial ELISA (BDSL,
Ayrshire, UK; 3); 12 (80%) of the samples were positive for PPRV.

Blood samples were collected on Nobuto filter strips (Advantec MFS
Inc., Tokyo, Japan) and transported to the BioSafety Level 3 laboratory
at the National Veterinary Institute, Uppsala, Sweden, for nucleic acid
detection (4,5). RNA was eluted from the blood impregnated filter strips
and screened for PPRV by using real-time RT-PCR specific for the N gene
(6). Viral RNA was detected in 13 (87%) of the samples, with most of the
positive samples indicating high viral load (cycle threshold <20).

For determination of the genetic lineage of detected viruses, RNA
from all samples was subjected to PCR amplification of a 351-bp segment
of the N gene by using the NP3/NP4 primer pair (7), but with a modified
protocol using the One-Step RT-PCR kit (QIAGEN, Hilden, Germany) (5).
Amplified PCR products were separated by electrophoresis, gel extracted,
purified, and processed for sequencing by using ABI PRISM BigDye
Terminator v3.1 kit (Applied Biosystems, Foster City, CA, USA),
according to the manufacturer's instructions.

N gene sequences were obtained from 10 (67%) of the samples, and
showed 83%-100% nt identity level compared with sequences available in
GenBank using the BLASTn tool (www.ncbi.nlm.nih.gov/blast) and 93%-100%
identity between each other. Phylogenetic analysis was performed with 4
representative sequences (GenBank accession nos. JN602079-JN602082) from
this study by using neighbor-joining and the Kimura 2-parameter model in
MEGA5 (CEMI, Tempe, AZ, USA), including N gene sequences representing
all 4 lineages.

The PPR viruses from Sierra Leone clustered in lineage II with
viruses from Mali, Nigeria, and Ghana, and could further be
distinguished into 2 clusters (Figure). One virus from Kabala clustered
closely with viruses from Mali (Mali 99/1), whereas all others showed
100% identity with a virus from Nigeria (Nig/75/1), in many countries
used as vaccine virus strain. In Sierra Leone at the time, however, PPR
vaccination was not being performed, suggesting that obtained sequences
originated from circulating field viruses related to Nig/75/1 rather
than being vaccine derived. This suggestion was strongly supported by
the clinical presentation typical of PPR. Surprisingly, no relationship
was found with PPRV strains so far described from Guinea, the immediate
neighboring country and closest livestock trading partner, or those from
Senegal, Guinea-Bissau, Cote d'Ivoire, and Burkina Faso, which
constitute lineage I.

[FIGURE OMITTED]

In conclusion, we confirm the presence of PPRV in Sierra Leone, and
provide genetic characterization of detected viruses, knowledge that is
fundamental for control, prevention, and in the long run, eradication of
the disease. The detection of 2 different sublineages at the livestock
market in Kabala shows how markets can serve as mixing vessels, and also
gives evidence of at least 2 separate introductions of PPRV into the
country, underlining the transboundary nature of the disease,
particularly in regions with uncontrolled livestock movements. Since
this study, an official vaccination program based on Nigeria/75/1 has
been launched.

Acknowledgments

We thank Hermann Unger for providing the PPRV cELISA.

The training mission was financed by the Swedish International
Development and Cooperation Agency Reference Group for Animal Health,
and cofinanced by the EC FP6 projects FLUTRAIN (www. flutrain.eu) and
EPIZONE (Contract No. FOOD-CT-2006-016236), work package 4.4,
(http://epizone-eu.net).